Crawler tread mechanism



May 2, 1933. G. c. JETT CRAWLER TREAD MECHANISM Filed June 6. 1928 3 Sheets-Sheet v1 NFS M JlLrnlr-lllv P L waabd' l ii I E Orl/MV S K ilk@ ATTQRNEY.

May 2, 1933. G. c. JETT' 1,906,610

CRAWLER TRED MECHANISM Filed June 6, 1928 3 Sheets-Sheet 2 IN VEN TOR. 550555' i." JETQ:

BY ,af/@MMM A TTORNE Y.

May 2, 1933. C.;t Q JETT 1,906,610

CRAWLER TREAD MECHANI SM Filed June S, 1928 3 Sheets-Sheet 5 I N VEN TOR. S'E'DREE ZL/iva:

lATTORNEY.

Patented May 2, 1933' UNITED@ s'rsrl-:vsf`

GEORGE c. JETT, or MILWAUKEE, WISCONSIN, AssIGfNoR oFgTwo-FIFTHsro vvanfrnn liniaal@ PATENT goI-rlclszg H. s'rIEMKE, or MrLwAUKEE, WISCONSIN CRAWLER TREAD livrEoHANIsivr Application ined nine 6,

This invention` relates to crawler tread mechanisms primarily for 'use as Wheel substitutes for trailer trucks, and to self-sustaining or truss type tread belts therefor.

A crawler tread mechanism, involvingr a tread belt of the character mentioned, is fully' the tread belt. f

In an effort to avoid this bumpy action attempts have been made to maintain sufficient slack in the opposite end loops of the tread belt to permit each shoe -to lower into its trussed or load sustaining yposition before re- -f ceiving the forward load carrying roller or tumbler and, similarly, to permit each shoe to remain intrussed or loadsustammg position until the rear load carrying roller or tumbler leaves the same. This use of a slack belt however is not a satisfa'ctorysolution to the problem, because in operation, particularly over soft ground, the slackin the forward end loop disappears due to the drag of the belt on the rollers, with theresult Vthat each forward roller or tumbler climbs upwardly upon the successive forward shoes and then falls with each shoe into its trussed position, producing the very action which it is attempted to avoid, and also imposing. severe strains and shocks on the belt structure.

One object of they resent invention is the provision of a craw er tread mechanism of the character mentioned in which the parts are so constructed and arranged as toavoid transmission of this bumpy raction to the supported load.

Another object is the provision in a crawler tread mechanism of resilient means for normally maintaining a definite spacing between the end rollers or tumblers but'yieldable upon the intrusion of excessive foreign matter to thereby prevent clogging.

Another object is the provision of a truss type tread belt for crawler tread mechanisms 1928. Serial No. 283,184.

involving hingedly connected shoes designed to closely conform to the peripheriesofthe end rollers or tumblers. y

Another object isthe provision of ian improved truss type tread belt of highcapacity y and Aof rugged, simple and economical design. s n

Other objects and advantages will appear from the following description of an illustrative embodiment of the present invention.

In the drawings Figure 1 `is a view in sideelevation, partly in section, of a crawler tread mechanism constructedin accordance with the present invention. y

Fig. 2 is a View in horizontal section.

Fig. 3 is a view in side elevation, partly in section, onfa larger scale, of a portion ofthe tread belt shown in Figure 1.

Fig. 4 is ay view in plan. of the treadl belt shown in Figure 3.

Fig. 5 1s a detail View 1n sectionof one of the truss links,

x Fig.`6 is a sectional view taken upon they moved. 1 V

Fig.V 7 is a view in side elevation of the spring'. loaded yoke shown in Figures l, 2 and 6. f al Fig. 8 yis a Afragmentary diagrammatic line '6-6 of 'Figure2 with the end roller reillustrating the action thereof during travel of the tread mechanism. f

The `crawler tread mechanism shown comprises an auxiliary Vframe 10 pivotally so View 'of the tread belt and coacting rollers y mounted intermediate its ends upon a horizontal pintle 11, rigidly anchored at one end k12 in an appropriate bracket 13 fixed to the bottom 14 of the vehicle body. ln: this instance the frame is in the form of a onepiece H-shaped casting having a pair of laterally spaced, substantially parallel, longitudinal members 15,*inte'grally and rigidly connected intermediatetheir ends by a hollow cross member 16, which contains a bushing 17 `fashioned to receive and form a bearing for the pintle` 11. The inner end 12 of the pintle is preferably tapered as indicated and threaded to receive a nut 18 by which it maybe drawn into a tight wedge iitwithin the bracket 13, the outer end of the pintle being reduced and threaded to receive a nut 19 and washer 20 to retain the same within the bushing 17 and member 16.

A pair of end rollers or tumblers l and 22, mounted at opposite ends ot the trame, between the longitudinal members 15, constitute a support and guide tor the endless tread belt 23 to be hereinafter described. The rollers shown are substantially the same as those described in my copending application hereinabove identiiied. Each comprises a pair of spaced parallel rims 2a integrally connected through the iorlred ends 25 of a series of spokes 26 which project radially from a relatively long hub 27. loller 21 is journaled upon a bushing 28 which is tightly clamped between the adjacent ends 29 ot' the members 15 by a shalt 30 in the form of a heavy tie-bolt extended therethrough. An integral iange 81 on one end of the bushing cooperates with a spacer washer 32 at the other end to confine the hub 27 against end play. The other roller 22 is similarly journaled upon a bushing 38 which is clamped between a pair of slide blocks 34C by a shaft 35 in the 'orm ot a tiebolt extended therethrough. Blocks are snugly Fitted for adjustment within longitudinal slots 36 'termed in the adjacent ends 37 of the longitudinal members 15, so that roller 22 is adjustable toward and from the other roller 22.

Provision is made in the mechanism shown for normally maintaining a definite spacing between the rollers 21 and 22 dur ing normal travel, but permitting the roller 22 to approach the roller 21 upon the intrir sion of excessive foreign matter between the tread belt and rollers to thereby prevent clogging. ln this instance this accomplished by the use of a spring pressed yoke 38, disposed within the frame 10 between the roller 22 and cross member 1G, and provided with a pair ot parallel legs 39 whose forward ends 40 are interposed between the blocks 34 and bushing and are perforated to receive the shaft 85. The legs 39 are guided in appropriate longitudinal channels 41 formed in the longitudinal member 15 of the frame. rlhe yoke is Valso provided with a substantially lli-shaped stirrup 42, which projects forwardly into the space between the rims 2d ot roller 22 and provides a support for and partially houses a heavy compression spring 48, interposed between the cross member 16.01E tl e trame and the end le of the stirrup. The .sprinoa 43 projects through an opening 15 in the yoke and is seated at one end upon a lug 46, projecting from member 12 and preferably grooved to receive the end convolution et the spring7 and to which the spring is securely anchored by appropriate means such as a clamp l? and screw 48. The other end of the spring engages an appropriate centering lug t9 in the stirrup. The arrzmgement is such that the pressure ot the spring` Li3 is transmitted thru the yoke to the shaft 35 to urge the roller 22 outwardly. A. pair of adjusting screws 50, threaded through lugs 51 ou the ends of the longitudinal members 15, coacts with the blocks ll to positively limit the outward movement of the roller, so that a 'predetermined spacing is normally maine tained between the end rollers. The screws are normally so set as to remove all slacl; from the tread belt without imposing any tension therein. ln the event of intrusion of excessive foreign matter between the rollers and tread belt however, the roller 22 may move in fardly against the pressure oi" the spring' 43, to thereby reduce the distance between roller centersand thus provide a slack in the tread belt suiiicient to prevent clogging.

The tread belt is of the self-sustaining or truss type and comprises a series of hingedly connected shoes so constructed and arranged as to closely conform to the periphery oi the rollers throughout the end loops oi' the belt and to provide a rigil load sustaining structure spanning the between the end rollers. ln this instance each shoe is in the form of a hollow casting shaped to provide a relatively broad tread surface 52 for cor.- tact with the ground, and a pair ot roller engaging surfaces which are separated by an upstanding guide portion 54 tor engagement between the parallel rims 2e ol the end'rollers. Surfaces are curved through the major portieri oi their length to match the curvature. of the rims :wl or" the rollers to increase the contact area therebetween and to thereby insure snug contact between the shoes and rollers throughout the end loops oi the tread belts; and the surfaces 52 prefierably concentrically curved with respect to the surfaces 53 so as to form a substantially continuous circular' surface concentric with respect to the roller centers throughout the end loops of the belt. The several shoes are connected by pivot pins 55 which entend through sets of inter-meshing ears 56 and 57 projecting from the adjacent edges ot successive shoes. Each pivot pin is fixed in ears 56 ot one shoe by appropriate means such as a locking pin 59, and is journaled in bushings G0 seated in the ears et' the adjacent shoe. In this instance each bushing 60 is formed from tiat .material curled into the torni indicated and each is held against rotation within the ear by a rib 61 which projects inwardly between the spaced ends of the curled bushing.

In the` tread belt shown the hinge action between shoes is limited by means which will now be described. ln this instance the guide portion 54 of each shoe merges into a'pair of spaced arms G2 which project upwardly loi) therefrom at the ends thereof. The arms 62 of each shoe are preferably braced by ,a tie rod 63' which extends through andconnects the upper endsl thereof.' Theadjacent arms of successive shoes are connected by an embracing'link 64.V Each link 64 comprises ar lpair of longitudinal bars 65 integrally connected at opposite ends by kcross bars 66,V

which coact with the inner ,faces '67 of the arms 62 to limit the hinge action between' successive shoes. l Eachy link 64 is preferably supported upon a pair of depending `legs 68 perforated as at 69 to receive the pivot pin 55l connecting the associated shoes. By mounting each link 64 Vin this' ymanner a proper relation yis always maintainedL be`- tween these links and arms` 625 A'limited hinge action betweenthe successive shoes is thus provided 4by which the tread belt is free `to wrap closely about each end roller 1 throughout each end loop of the belt and by pitch, or distance between the centers oii pivot pins 55, that the upper and lower runs of the tread belt assume aslightly cambered convex form. The several pivot pins contained within the lower run of the belt thus lie within the arc A-Aof a circle (hereinafter referred to as the cambered pin circle)` having a radius severaly times that of the rollers 21 and 22.

. The operation of thetread .mechanism shown will now be described, reference beingv had particularly to Figure 8. During.

travel of the tread mechanism from left to right in Figure 8, each of the several shoes contained in theforwardend loopof the tread Vbelt remains tightly wrappedr Y, about the periphery of the forward roller 21. and each movesk asa unit with the roller until it arrives in load sustaining posiv tion beneath the roller and'ultimately assumes a trussed'y position withrespect to an x adjacent yshoe and thereby'becomes apart of the rigid structure spanning the gap between the rollers. vThe action of each shoe as it approaches this trussed position is il-r L' position shown. Thereafter the roller 21" swings upwardly from the shoe 23m over the next ivot pin andultimately'forces the next s oefdownwardly into trussed position.

, Afterr leaving the orwardroller in the' v manner described each shoe remainsa party ofthe rigid truss structure spanning the gap between the rollers until itis wrapped upon the rear .roller 22 yand lifted out of trussed relation with respect to theneXt adjacent shoe. The fullA and dotted line positions of shoe 233/ illustrate the action of each shoe asit leaves this trussed position. As indicated, itvbe'ars firmly againstthe roller 22 and swings upwardly ktherewith about the pivot'pin kg/from the full line to ithe dotted line position. As` the roller v 22 continues. to advancev it` swings downwardly about the ypivot ypin shoe.V f v l It willthus be noted that the several shoes engage the rollers-211and22 by apure' wrap-` lai) 55g/ until 4seated upon thefrnext ping and unwrapping action so that rolling `friction and consequent wear therebetween is reduced to a minimum. It will also be noted that eachroller, in passing from shoe to shoe, swings: about" each intermediate pivot'pin 55 as acenter, causing each roller to periodically rise and fall throughr a den; nite distance.' Inl orderrto avoid transmitting thisfvertical bumpy action to the supported load the distance between rollercentersV is sorproportionedwith respectto the shoe lpitchthat, both rollers rise S and .fall simultaneously in opposite phase. In .other words whenV roller 21 is inV lowest position roller'g22 is in highest position and ,vice

versa and the truck frame 10 swingsr as a simple lever .upony the pintel 11 without `raislng or loweringthesame. A proper proportioning ofthe parts for this action q maybe .obtamed by the following process.

'First lay out thearc A-A .representing e the cambered pin circle of desired curvature. The radius of thisfarc Vis ordinarily about fifteen times the radiusy of the end rollers. Then erect a radius R-R normal to this arc, and, at a distance from theline R-R offabout one-half the desired spacing e yof line B--B with the'arc A-Aywill repre-y sent the center of the pivot pin 55m. Then,

havingr selected the desired shoespitch, locate v a point d on the arc A-,A at a distance approximating the desired distance between roller' centers and equal to an integral numberof shoe pitches from the point b. Point c represents the center-lof pivot vpin 553/.

Then at a point Z on'arc A-A at a distance equal kto a half shoe pitch from point 0 erect a .line D-'Dk along a radius of arcy A-A. Then select atrialV point b upon *p the line B--B to represent the ,center vof roller .21, `and thereafter locate a point d on theradiuslineID-D ata distance from,

point c equal to the distance between points l) and b. Point cl then represents a trial center for roller 22. Then lay out the en* tire tread belt tightly about therollers 21 and 22, and if an integral number of shoe pitches does not bring the belt to a close, it will be necessary to relocate the points d" and of, in accordance with the above rule, and again lay out the entire tread belt. After repeated trials a closed tread belt will be obtained equal in length to an integral number of shoe pitches and the finally established points d and b will represent the correct positions of the roller centers. It will of course be understood .that in laying out the tread belt about the rollers 21 and 22 the centers of the several pivot pins within each end loop of the belt will lie in the arc of a circle m or a whose center is the trial point Z or b and Whose radius is equal to the distance between points b and b', and that the centers of the several pivot pins in the upper run of the belt will be in an are similar to arc A-A and tangent to the end circles m and n just defined. It will also be understood that in some designs the line A-A may be a straight line, (an are of infinite radius) in which event line D-D would be erected normal to line A-A and consequently parallel to lines R-R and BB.

Various changes may be made in the embodiment of the invention hereinabove specifically described without departingfrom or sacriiicing any of the advantages of the invention as defined in the appended claims.

I claim l. In a crawler tread mechanism the combination of a load carrying member, a pair of load sustaining rollers, a load transmitting frame connecting said rollers, an endless tread belt trained about said rollers, said tread belt comprising a series of hingedly connected shoes having roller receiving rsurfaces shaped to match the peripherics of said rollers and coacting with said rollers to eliect vertical oscillation thereof, the spacing of said roller centers being so related to the length of said shoes that said roller oscillations occur simultaneously7 in opposite phase relation, and a load transmitting rockable connection between said member aiid frame permitting` free vertical oscillation of said frame about an axis intermediate said rollers and through which the vertical oscillation of each roller is substantially compensated by that of the other.

2. In a crawler tread mechanism the com bination of a pair of load sustaining` rollers each having a substantiallycircular periphery, a series of hingedly connected shoes forming an endless treaal belt trained about said rollers, said shoes having roller receiving surfaces curved to match said roller peripheries and coacting with said rollers to effect ,vertical oscillation thereof, a load transmitting frame connecting said rollers and normally maintaining` a definite spacing between the axes of rotation thereof, the distancebetween the axes of said rollers being so proportioned relative tothe spacing be tween hinge centers of the successive shoes that the said vertical oscillation of said rollers occurs simultaneously but in opposite phase relation, a load carrying member, and a rockable connection between said member and frame permitting` vertical oscillation of said frame about an aXis intermediate the axes of said rollers.

3. In a crawler tread mechanism the combination of a pair of load sustaining rollers each having a substantially circular periphery, a series of hingedly connected shoes forming an endless tread belt trained about said rollers, means coacting with said shoes to limit the hinge action therebetween and thereby provide a rigid truss structure spanning the space between said rollers, said shoes having roller receiving surfaces curved to match said roller peripheries and coacting with said rollers to effect vertical oscillation thereof, the spacing of said roller centers being so related to the shoe pitch that said roller oscillations occur simultaneously in opposite phase relation, a load transmitting,` frame connecting said rollers, a load carrying member, and a load transmitting rockable connection between said member and frame permitting free vertical oscillation of said frame about an axis intermediate said rollers.

el. In a crawler tread mechanism the combination of a pair of load sustaining rollers each having' a substantially circular periphery, a truss type tread belt trained about said rollers and forming an outwardly cambered truss structure therebetween, said belt comprising a series of hingedly connected shoes having roller receiving surfaces curved to matclr said roller peripheries and coacting with said-rollers to elfect vertical oscillation thereof, thespacing of said roller centers being so related to the shoe pitch that said roller oscillations occur simultaneously in opposite phase relation, a load transn'iitting frame connecting said rollers, a load carrying member, and a load transmitting rockable connectionbetween said member and frame permitting free oscillation of said frame about a horizontal axis intermediate said rollers.

5. In a crawler tread mechanism the combination of a pair of load snstaining'rollers having circular geripheries, a series of tread shoesv connected to form a truss type tread Vbelt trainedabont said rollers, said shoes load transmitting frame connecting said rollers and normally maintaining a definite spacing between the axes of said rollers such` Y that when one of said rollers rests squarely f upon the roller receiving surface of one shoey in the trussed position of thatfshoe the other of said rollers is midway between other successive shoes to thereby effect vertical oscillation of said frame during lengthwisetravel of the mechanism, a load carrying member, s

and a rockable connection vbetween said member and frame for transmitting the load f to said frame at a point adjacent the axis of oscillation thereof. f

In witness whereof, I hereunto subscribe my name this 2nd day of June, r1928.

GEORGE o. JETT.; c 

